Our present invention relates to a rolling mill train with staggered (stepped-gap) mills, especially utilizing a tandem rolling configuration and wherein on both sides of the rolling line, mill stand walls are provided in windows of which the mill rolls are journaled in bearing chocks serving as bearing mounts and such that the mill rolls and their bearing mounts can be withdrawn from and replaced in the windows for roll replacement.
A tandem rolling system is described in EP 0 857 521 and the corresponding U.S. Pat. No. 5,979,206. That rolling train may also be referred to as a staggered-mill rolling train. The individual rolling stands of the tandem group or similar staggered mill stands for reversing or continuous operation are provided as individual stand units, each with a pair of mill rolls mounted in two stand walls and having respective traverses connecting the mill walls.
Because each pair of rolls is received in a respective pair of mill walls with respective traverses, the overall length of the rolling train must be a function of the number of mill stands provided, any spacing between the mill stands and the dimensions of the mill stands assigned to the individual pairs of rolls.
It is, of course, desirable to make the length of the rolling train as short as possible since relatively long rolling mill trains are associated with a variety of drawbacks. For example, the armatures which may be necessary to guide the rolled workpieces between the pairs of rolls frequently must be long. The passage of the workpieces across the spacings between the rolls is considerable and the productivity, in terms of output per unit time, can be limited.
The intervals between reversals can be significant in the case of reversing mills and high precision in the control of the speed is necessary for both continuous reversing mills where the spacings between the roll pairs are considerable. In most cases the roll changing procedures are time-consuming and when the duration of such procedures is multiplied by the number of mill stands and roll units which must be replaced, the down time of the rolling train can be considerable. Finally, the cost of the equipment required for the roll change, the stand structures themselves and the guides required between stands can be considerable as well.
It is, therefore, the principal object of the present invention to provide a staggered rolling train or tandem rolling train of the type described in the aforementioned patent, wherein, however, the capital and equipment cost can be reduced, the productivity increased and the length of the rolling train limited.
Another object of the invention is to provide an improved rolling train whereby drawbacks of the earlier systems can be avoided.
These objects are achieved, in accordance with the invention in a rolling train in which a workpiece traveling along a rolling line is rolled in succession between opposing mill rolls of a succession of pairs thereof, the mill train having at least one mill stand which comprises:
a pair of unitary stand walls spaced from the mill line on a drive side and a service side of the mill stand respectively, each of the stand walls having a plurality of stand windows spaced apart along the line and in a direction of rolling of the workpiece;
respective pairs of the mill rolls having bearing chocks received in corresponding ones of the windows of the pair of stand walls and journaling the respective mill rolls therein, the pairs of mill rolls and the respective bearing chocks being removable from and replaceable in the corresponding windows of the stand walls on the drive and service sides of the stand for roll replacement; and
respective intermediate traverses extending transversely to the direction and interconnecting the unitary walls between successive ones of the pairs of rolls and locking the stand walls together.
According to the invention, that mill stand can be incorporated in a staggered mill line or tandem rolling plant of the type described in the aforementioned patent.
According to this invention, a stand for a multiplicity, preferably at least three pairs of mill rolls spaced along the rolling line can be mounted in unitary stand walls on opposite sides of the rolling line and each of which is provided with a plurality of windows receiving respective pairs of rolls and their bearing mounting pieces, i.e. the so-called bearing chocks. Instead of having such walls for each pair of rolls and traverses bracing the walls of the separate mill stands, the present invention provides common intermediate traverses between the pairs of rolls of a single mill stand having unitary stand walls for a multiplicity of roll pairs, the intermediate traverses securing the stand walls together.
This construction enables relatively small distances between the pairs of rolls and, indeed a spacing between the pairs of rolls which can be a small fraction of the spacing which hitherto was required when each such pair of rolls was mounted in a separate stand.
As a result, the rolling and reversal times are significantly shorter. The distance over which the workpieces must be guided by rolling armatures between rolls can be significantly shorter and can be formed in one piece, thereby creating a cost saving. Furthermore, the system is of greater operational reliability and often a better rolling quality because shorter distances between successive pairs of rolls which must be bridged by the workpiece.
We have found that especially in the fabrication of H-section structural shapes, there is an improvement in the uniformity of the product and a reduction of off-centering of the flanges, for example.
Because the stand walls are common to a multiplicity of pairs of rolls, many individual operations can be eliminated or operations such as roll change can be effected for groups of rolls simultaneously and structural simplicity can be gained by eliminating additional traverses or the like as may be necessary by comparison with roll stands individual to the pairs of rolls.
In so-called duo stands which have hitherto required four tension anchors, traverses, clamping nuts and hydraulically actuated clamping wedges, numerous sole plates and hydraulic actuators and clamping devices and separate medium fittings for supplying the hydraulic medium, all of these duplicated elements can be eliminated in whole or in part by the common supply of hydraulic fluid to all of the actuators for the three or more roll pairs and the use of traverses between the roll pairs and thus common thereto.
According to a feature of the invention, at the ends of the stand walls in the direction of the rolling line, respective base plate clamping devices are provided. With the system of the invention, using such base plate clamping devices at the ends of each unitary wall, the greater number of base plates and respective clamps which would have been needed for a multiple wall system in the case of separate stands for each pair of rolls, can be eliminated.
The hydraulic fluid medium feed for the hydraulic actuators of the rolls can be provided with a single hydraulic medium network which can extend between the service side and the drive side walls. While reference is made here to at least one medium network, it will be understood that only one may be required. The single medium supply fitting can be provided for all of the actuators of the rolls mounted in the two walls. Separate medium networks and medium columns or fittings for each pair of rolls can be avoided.
A further simplification in accordance with the invention provides that between two neighboring roll pairs mounted on two walls of the invention, a common roll armature is provided. This armature can be significantly shorter than the roll armatures used to guide workpieces heretofore and can even be formed in one piece, thereby guiding the workpiece with high reliability and reducing the length of free space which would have to be bridged by the rolled workpiece between the roll pairs. This, of course, ensures a better rolling quality.
The common roll armature can be fixed on a roll beam which is disposed centrally between roll pairs of the multiple pair stand of the invention. As a consequence, additional roll guide devices and holding brackets which may be required where intermediate rolling stands are provided between main rolling stands, can be eliminated. The capital cost is greatly reduced, the span occupied by the number of roll pairs included in the two walls is reduced and operating costs are likewise reduced.
Since the stand walls are formed each in one piece, the retraction of a retractable stand wall is greatly simplified. According to the invention, the stand wall on the service side of the mill can be retracted, e.g. by an actuator such as a long hydraulic cylinder and the set of roll pairs mounted in the stand walls can be retracted in a similar direction onto a single carriage for the entire roll unit. The traverse connections can be opened, in that case, as can clamping devices at the base plates to enable the retraction of the service side wall. Alternatively, the roll pairs can be displaced by respective hydraulic cylinders onto one or more such carriages and the carriage or carriages can carry the rolls to be replaced away from the mill stand in a direction perpendicular to the retraction direction. A crane can be used for this purpose, as well. The replacement rolls, roll pairs or set or units of multiple roll pairs can be brought into line with the openings in the stand walls by the carriage or crane and the retractable wall can be replaced in its original position and locked to the traverses and the base plate.
It has been found to be advantageous to provide the roll pairs so that they are replaceable with the roll armatures and such that all of the roll pairs in the stand can be transported to the stand and away from the stand on a single carriage.
The roll pairs can be driven by meshing wheel transmissions which can be provided in a common housing for all roll pairs and the control for individual roll pairs can remain unaffected.
Upon a roll replacement and the retraction of the service side stand wall, the actuator or hydraulic cylinder should have a greater length than is required for extraction of the roll unit or set.